Plasma arc torches, also known as electric arc torches, are commonly used for cutting, marking, gouging, and welding metal workpieces by directing a high energy plasma stream consisting of ionized gas particles toward the workpiece. In a typical plasma arc torch, the gas to be ionized is supplied to a distal end of the torch and flows past an electrode before exiting through an orifice in the tip, or nozzle, of the plasma arc torch. The electrode has a relatively negative potential and operates as a cathode. Conversely, the torch tip constitutes a relatively positive potential and operates as an anode. Further, the electrode is in a spaced relationship with the tip, thereby creating a gap, at the distal end of the torch.
In operation, a pilot arc is created in the gap between the electrode and the tip, which heats and subsequently ionizes the gas. Further, the ionized gas is blown out of the torch and appears as a plasma stream that extends distally off the tip. As the distal end of the torch is moved to a position close to the workpiece, the arc jumps or transfers from the torch tip to the workpiece because the impedance of the workpiece to ground is lower than the impedance of the torch tip to ground. Accordingly, the workpiece serves as the anode, and the plasma arc torch is operated in a “transferred arc” mode.
Plasma arc torches often operate at high current levels and high temperatures. Accordingly, torch components and consumables must be properly cooled in order to prevent damage or malfunction and to increase the operating life and cutting accuracy of the plasma arc torch. To provide such cooling, high current plasma arc torches are generally water cooled, although additional cooling fluids may be employed, wherein coolant supply and return tubes are provided to cycle the flow of cooling fluid through the torch.
Several plasma arc torches cool electrodes by delivering a flow of coolant to an internal surface of the electrode. Because the shape and size of the coolant flow path to the electrode can significantly affect (i.e., increase or decrease) electrode operating life, it is not uncommon for coolant flow paths to be advantageously shaped and sized for a particular electrode size in order to maximize, or at least increase, electrode operating life.
Some plasma arc torches are adapted to house a variety of electrodes of different sizes for cutting various materials at different amperages. Because the different electrode sizes change the characteristics of the coolant flow path, the coolant flow path in these torches is not optimized for any one electrode size. Instead, the design of the coolant flow path is a compromise of performance for the various electrode sizes.
Accordingly, the inventors have a recognized a need for devices and methods that allow electrodes of different sizes to be installed in a plasma arc torch with a same coolant flow path being maintained regardless of which of the differently sized electrodes is installed on the torch.
Additionally, an unwanted flow of coolant commonly occurs when components are not installed on the plasma arc torch such as during component replacement. Accordingly, the inventors have recognized a further need for devices and methods for preventing the flow of coolant when no electrode is in installed on the plasma arc torch.